Even though Chicago has recently experienced some of its lowest temperatures in two years, transit agencies said Wednesday they've been able so far to dodge the arctic bullet and avoid major problems.

CTA riders have shivered through this week's deep freeze with minimal delays because the fleet of buses and trains is gradually getting younger as the transit agency focuses on overhauling deteriorated rail equipment, officials said.

Although winter brings the most weather-related delays, Metra says it has succeeded in keeping equipment from succumbing to the bitter cold.

Pace, meanwhile, reported no significant delays due to the cold, also crediting preventive maintenance, not to mention the benefits of parking in warm garages.

Here's a rundown on how the transit agencies say they have performed in the deep freeze — and how commuters have fared:

'CTA's priority'

CTA officials point to a small number of weather-related incidents, including a cracked rail on the south branch of the Red Line and defective train doors and brakes that affected service on the Brown and Purple lines during the Tuesday morning rush.

Extreme cold can cause more problems than just snow for trains, officials said, because of the increased risk that moving parts, like track switches, could seize up and electronics that operate switches and track signals could fail.

Heating system checks are made on trains and buses before they enter service during winter, and not only on brutally cold days, officials said. CTA standards call for a minimum interior temperature of 68 degrees, although several Blue Line riders called the Tribune this week complaining about cold trains.

But the longest disruption does not appear to be linked to the cold, officials said. The mishap, which trapped Blue Line riders in the bitter cold after midnight Monday, was caused by the electrified third rail becoming dislodged on part of the O'Hare branch.

The problem shut down service for almost two hours between the Cumberland and Jefferson Park stations, complained some riders traveling inbound from O'Hare International Airport. They said that after passengers on a stranded outbound train were evacuated and transferred via planks to their train, the train switched directions and headed to the Rosemont station.

The CTA was slow to provide alternative service on shuttle buses during the rail service outage, riders said.

"It seemed like the CTA's priority is the equipment and not the passengers," said Bob Pierce, 53.

The CTA apologized. "It was an unfortunate alignment of circumstances that evening for our customers,'' Chase said.

Metra's 'fail-safe' system

Over the past three days, the commuter rail agency has tallied about three dozen cold-related delays on seven lines out of more than 700 trains a day, Metra said.

Metra's goal for overall system on-time performance is 95 percent, and it generally hits that mark regardless of the season, according to data posted on the agency's website.

Metra considers a train on time if it arrives at its final destination within five minutes of its scheduled time.

From December 2011 to March 2012, performance ranged from 94.3 percent to 97.4 percent, although last winter was relatively mild.

"There's a lot to prepare for in order to handle the extreme cold weather," said Don Orseno, Metra's chief operations officer. "So far, I think we're doing pretty good, actually."

Broken rails were blamed in many of the incidents, including 15 delays Monday on the BNSF line, spokesman Michael Gillis said.

A crack in a rail might measure only a fraction of an inch, but that's enough to change signals from green to red and halt trains, said Orseno, who described it as a "fail-safe" system.

Commuter Andy Karas, 50, said that even though he was delayed only one time this week, he was stunned to get more than 200 text alerts from Metra about service problems.

"It was incredible to me that there was that much trouble," said Karas, of La Grange. "It's the usual story, right? They know that switches are subject to the cold. Why can't they do something proactive about it?"

Switches have such close tolerance that the slightest expansion or contraction, and even frost, can cause them to malfunction, Orseno said. Metra uses heaters to keep switches operating properly.

Cold weather also can cause delays simply because people who are bundled up move more slowly, or tend to wait inside warm cars or stations until the last minute before boarding a train, Metra says.

Regardless of delays, Bob Dahl, 47, said he recently quit driving downtown because the train is more reliable.

"They've been on time. Everything's been great. I've had no issues whatsoever," Dahl said.

Newer Pace buses

Pace's strategy for dealing with cold conditions is to rely heavily on preventive maintenance to ensure that vehicles run at peak efficiency and are less prone to breakdowns, spokesman Patrick Wilmot said.

Pace also stores the majority of its buses indoors so they can be started easier and experience less exposure to extreme weather, he said.

"Also, we've taken delivery of some newer buses in recent years that naturally are more reliable than the older ones they've replaced due to their age," Wilmot said.